Speed kills

Do you get any slip-stream effect at that distance, or is this to avoid impeding traffic?

 

Traffic dictates how far I'll go so I when possible go around rush hour. 50 is usually as low as I go on freeways.

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In regards to Don mentioning the press on hypermilers, it's a lot like the press on the Prius. Both the Prius and hypermiling have writers that are gearheads and simply won't give fair coverage - even spread falsehoods.

 

At 60 mph, the Two Second rule requires 176 feet, which happens to be a few inches more than 12 Prius lengths. When using trucks as protection against speedballs, I prefer to leave twice this distance, reducing stress fatigue.

But apparently Two Seconds has been unrealistic in so many places for such a long time that when news media interviewed drivers caught by a tailgating emphasis patrol, many had never heard of it. Or that 2 cars lengths was unsafe.

 

Even so, there are a lot of people talking against hypermiling that have not given it a fair trial, quoting articles that are also slanted against it.

....so I feel guilty I have not caused a ten car pile up within the past three years like I'm supposed to do.

 

To me, if the Prius requires significantly altering my driving style (including driving 10-15 miles slower than traffic) then the claims of good gas mileage are bogus. You can always come up with "tricks" to get better mileage. One is to only drive inside a building on rollers with no wind resistance and the air and heat off (e.g., the EPA method). Another is to always drive in the draft of a truck, or to never drive in bad (excessively hot or cold) weather.

I drive normally and accept the mileage I get. With hard-core winter tires and driving the ups-and-downs here in Colorado that can be as low as 37 MPG for a tank average, which is common this winter. In a year of ownership I have never seen better than 42 MPG for a tank average even when driving in Oklahoma on vacation (relatively flat and lower altitude). Therefore, for me this is "normal" mileage. Any attempt to get better mileage would require significantly altering my driving style, giving up heat or air, or giving up some level of safety.

I used to get this good with my Renault R5 in the 1980's. However, the Renault was a lightweight noisy box with no power anything. To get this good a mileage with a larger, heavy car with luxury features is, to me, acceptable. I will admit, however, the Renault rode SIGNIFICANTLY better than the Prius . Gotta love the French and their soft suspensions!

 

Consider that the EPA rates the Prius at around 45 mpg when the average US vehicle gets 21. Not bad, but 60mpg @ 60mph on the freeway is possible (speaking from experience).

Source: EPA

Note the reasons the average American's fuel economy has stalled at 21mpg:

- Weight increased from 3200 to 4100 pounds.

- 0 to 60 time has decreased by 5 seconds

- Fewer manual tranmissions on non-hybrids

- More trucks as personal vehicles.

 

Thanks, Chuck. I agree with your assessment. In re-reading my own post it sounds a bit irate, although it wasn't meant to. I just don't see the EPA mileage numbers as very accurate (and it might be worse on hybrids).

I also agree that there is a big difference between 60 MPH economy and 75 MPH. Not to mention my commute goes from about 5300 foot altitude to about 7600 each day. You would think I would gain back coming down what I lose going up, but even my base altitude is probably hard on economy (3 percent per thousand foot altitude loss of efficiency gives a 15 percent loss for the ICE at my altitude, and over 20 going over Monument Pass). I would rather get near 40 and drive "normally" than try to get 50 in these hills and at this altitude.

 

If anyone wants the 101-page EPA report, it's a PDF > http://www.epa.gov/otaq/cert/mpg/fetrends/420r06011.pdf

Just thought a snippet executive summary on pages 5-11 would suffice.

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Agreed: driving in or near the Rockies is different.

 

Be interesting to see this on the same grid with a BobWilson4web Prius mpg vs speed graph. First, Prius about 4 times as high at 20 mph and still twice as high at 60 mph.

Also, the shape of the Prius curve with its lack of gears is striking compared to this non-hybrid beast.

 

It would also be interesting to see it with manual and automatic transmissions separated. I know that my manuals don't peak at as high a speed as indicated by this graph.

I didn't keep consistent fuel logs in my automatic days. Tried to, but it was corrupted by family members who wouldn't cooperate.

 

That rule of 3 percent loss per thousand feet is for power, not efficiency.

Efficiency actually improves at high altitude, especially in non-hybrids. Mine do better in Colorado and Wyoming than down here at sea level. The altitude difference is less in hybrids because the Atkinson cycle sharply reduces the 'pumping' loss that hurts sea-level efficiency in Otto cycle engines.

As for 'gain back coming down what I lose going up,' my Prius does exactly that -- IF the downhill is not so steep that it requires friction brakes or engine braking. A number of your hills are too steep for that energy recapture.

 

Rain / slush (snow) kills MPG even worse than speed.

I also like to follow 18 wheeler's, not to draft, but because they don't drive like jerks. A predictable vehicle in front of you means no braking.

In bumper-to-bumper traffic, it's better in front of them, they don't mind when you P&G, if they can't get past 2nd gear.